The invention relates to a method of forming a sheet metal cup, and more particularly to a method of forming a sheet metal cup without using a mandrel.
Metal cups, used as pulleys and idlers, may be formed by spinning or metal forming a flat, circular metal blank or a metal blank with a hub. The flat blank is placed in a spinning machine, where it is generally held in place by clamping chucks. A central mandrel or tailstock is pressed against a center of the blank. A mandrel is also put in an axial position to support the blank across its entire width. The blank is spun while forming rollers are moved radially about the blank, while it is supported by the mandrel. As the forming rollers move inward, metal may be collected and accumulated against the central mandrel, forming a hub. The forming process imposes significant side loads on the central mandrel, thereby requiring it and the associated machinery to have a thickness sufficient to resist deformation.
Representative of the art is U.S. Pat. No. 5,947,853 (1999) to Hodjat et al., which discloses a pulley having an integral hub that is spun formed of a flat disc of sheet metal. As the metal is gathered toward the pulley hub across a supporting mandrel, a central mandrel controls the location and size of a hub.
Also representative of the art is U.S. Pat. No. 4,404,829 (1983) to Dorakovski which discloses a process of manufacturing a pulley using a cup-shaped blank. The cup shaped blank is clamped between a feeding plunger and a tail stock assembly. The tailstock fully engages and supports the blank as it is formed into a ribbed pulley.
Use of a sufficiently thick mandrel in the prior art imposes restrictions on the blank cup size. For example, to make automotive pulleys with a commonly used bearing that has an outside diameter of 40 mm, the pulley diameter cannot be less than about 64 mm. This is because the mandrel thickness cannot be less than 8 mm, otherwise it will break during the forming process.
What is needed is a method of forming a sheet metal cup without using a mandrel. What is needed is a method of forming a sheet metal cup without using a mandrel for forming a small radius cup. The present invention meets these needs.
The primary aspect of the invention is to provide a method of forming a sheet metal cup without using a mandrel.
Another aspect of the invention is to provide a method of forming a sheet metal cup without using a mandrel for forming a small radius cup.
Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings.
The invention comprises a method of forming a sheet metal cup without using a mandrel. A cup shaped blank is first produced having a relief on a rim outer circumference.: The blank is clamped in the spinning machine. The relief controls and facilitates the bending process, creating a uniform curve at a predetermined bending point. During the rolling process, a forming roller is engaged with rim, and is moved progressively parallel with an axis of rotation. As the forming roller moves, the rim is progressively bent from an orientation normal to an axis of rotation to a position parallel to the axis of rotation. The fully formed rim can then be punched, if necessary, to accommodate a bearing or shaft. This allows a small radius cup, which can then be used as a pulley or idler, to be formed without use of a mandrel.